<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        body {
            margin: 0;
            padding: 0;
        }
        div {
            width: 100px;
            height: 100px;
        }
        div:nth-child(1) {
            position: relative;
            background: red;
            z-index: 6;

        }
        div:nth-child(2) {
            position: relative;
            background: yellow;
            z-index: 7;
        }



        div:nth-child(3) {
            background: blue;
        }

        #c-1{
            position: absolute;
            top:300px;
            left: 300px;
            width: 30px;
            height: 30px;
            background: black;
            z-index: 100000;
        }
          #c1-1{
              position: absolute;
              top:220px;
              left: 300px;
            width: 30px;
            height: 30px;
            background: pink;
        }


    </style>
</head>
<body>
    <div class="c">
        <div id="c-1"></div>

    </div>
    <div class="c1">
        <div id="c1-1"></div>
    </div>
    <div class="c2">3</div>

</body>
</html>